Melissa Block speaks with Sid Perkins, a freelance writer specializing in earth sciences, about the recent discovery of a "lost microcontinent" submerged beneath the Indian Ocean.

MELISSA BLOCK, HOST:

Deep underwater, entombed under layers of volcanic rock on the Indian Ocean floor lurks a ghost continent, or at least that's what a team of geologists now thinks. Among the clues are tiny crystals found in the sand on island beaches. The scientists called the ancient continent Mauritia. They believe it broke away from India and Madagascar and sank into the seabed tens of millions of years ago.

This is all laid out in a new scientific paper, and Sid Perkins of the journal Nature joins me to explain what the scientists found. Sid, welcome to the program.

SID PERKINS: Hi. Thank you.

BLOCK: And why don't you paint a little bit more of this picture for us? This ancient continent that scientists think now is resting at the bottom of the Indian Ocean, where exactly do they say it is?

PERKINS: Well, when you look at the ocean floor between Madagascar and India, there are areas that are rather broad and much thicker than the normal ocean crust. Ocean crust is typically 5 to 10 kilometers thick, and these are substantial areas that are somewhere between 25 and 30 kilometers thick. And they probably add up to something that was about the size of the nation of Costa Rica altogether.

BLOCK: So pretty tight. They're calling it a microcontinent.

PERKINS: Yes, yes. It's a microcontinent. And what they're looking at is, again, when tectonic activity kind of ripped apart Madagascar and India, India kept going, crashed into South Asia. Madagascar was left behind kind of close to the African continent. And then what this continent of Mauritia is presumed to be was a kind of a small fragment or an archipelago that was kind of abandoned in between the two. And as the ocean crusts thinned, those bits were fragmented and then submerged, and then now they're at the bottom of the ocean.

BLOCK: We mentioned that the scientists are looking for clues, and they found them, they think, in these tiny crystals in sand on beaches, on the island of Mauritius. What was it about those crystals that made them think, aha, there's a lost continent on the ocean floor?

PERKINS: The crystals that they found are vastly older than they believe the island to be. So if the island was nothing but, you know, lava erupted to the surface and then waves beat on the lava, you expect the sands that you find to be no older than the island itself. But what they found instead were these zircons that were anywhere from 660 million to 2 billion years old, which is vastly older than the island is presumed to be, which is only around 10 million years.

BLOCK: Let me see if I understand this right. Is the idea that the only way to explain how these zircon crystals ended up on the sands of Mauritius, is the only explanation for that that they came from part of the continental crust that is actually on the ocean floor, this lost continent that we're talking about?

PERKINS: Yes. They're saying that they weren't brought in by human activity. They were windblown. So the mystery is to figure out where these zircons came from. They're saying that - process of elimination of all the other things that they don't think is likely - that these zircons were actually brought up from the ocean floor. When the lava was erupting to the surface, it snatched bits of fragments of that ancient continental crust that had been buried on the seafloor and then brought unto the surface to be subsequently found on the beach.

BLOCK: Do scientists assume that there are lots and lots of lost continents that are on the ocean floor?

PERKINS: Sure. When I talked to one of the scientists, he was saying well, you know, it's very likely that these are kind of a common thing scattered across all the ocean basins where you've got ocean floor spreading that, you know, had ripped things apart.

BLOCK: Sid Perkins, thanks so much for talking to us.

PERKINS: OK. Thank you, ma'am.

BLOCK: Sid Perkins has written in the journal Nature about a lost continent believed to be on the floor of the Indian Ocean. That research appears in the publication Nature Geoscience.

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